Goal To observe the way a wave propagates on the surface of water.. Items required:

a container with water (preferably of large diameter) a toothpick or stick an elongated object such as a ruler

The method of the experiment

1. Pour water into the container.
2. Dip the stick into the middle of the vessel and observe the surface.
3. Dip the stick closer to the edge and observe the surface.
4. Immerse the ruler and observe the surface.
5. Blow on the surface and observe the surface.

Observations During the immersion of the stick, concentric circles spreading from the source of the disturbance (the stick) towards the edges of the vessel appear on the surface. When the waves reach the border, they bounce and move in the opposite direction, which can be seen better by submerging the stick closer to the edge of the vessel. The more time passes, the less visible the disturbance on the surface. When a longitudinal object is submerged the waves are not perfectly round but form a flat wave. When blowing, the shape is highly irregular and the waves move in different directions from the blowing point. Conclusions Depending on the type of disturbance, waves on water can take different shapes. Point disorders form a circular wave, whereas linear disorders form a flat wave. This results from the fact that each single point of the disturbance is a source of a circular wave, which as a result of overlapping (interference) constitutes a flat wave. The introduction of an irregular disturbance causes a series of waves spreading in different directions. Explanation Water molecules are attracted to each other by electromagnetic effects. Each water molecule is subjected to cohesive forces that are balanced in the entire volume of the liquid, but on the surface the resultant force is directed perpendicularly to the liquid-solid, liquid-gas or liquid-liquid interface and is called surface tension force. At the boundary between two centres, e.g. liquid-vacuum, liquid-gas or liquid-liquid, a so-called liquid-free surface is formed. Depending on the forces applied, it can take different shapes. Examples include the surface of a drop, the surface of a sea/lake, or the surface of water on glass. Under the influence of an additional external force, this free surface can be disturbed, e.g. by a gust of wind, a cone falling into a lake, a boat passing through or an underwater earthquake. As a result of such events, liquid particles start to move in place but are not moved further. Only the energy and momentum generated during the disturbance is transported, but not the mass. If the particles move perpendicularly to the direction of the disturbance, this is called a transverse wave. If, on the other hand, the direction of movement of the particles is in line with the direction of the disturbance, we are dealing with a longitudinal wave. On the sea’s surface, water molecules often also move in small circles. The vibrations of particles and their oscillations around an equilibrium position on the surface are seen as a wave that propagates in all directions from the source of the disturbance. Due to the gradual loss of energy caused by friction forces, the further away from the source of the disturbance and over time, the less particles will lean out of balance, and thus the wave will slowly fade away. Depending on the shape of the source of the disturbance (point, linear), the shape of the propagating wave will differ. Additional information: Jerzy Dera, Fizyka Morza, Wydawnictwo Naukowe PWN, Warszawa 2003, ISBN: 83-01-14020-8